"At this point, we need probable cause of a crime. And the existence of probable cause is painstakingly clear to everyone."

Merritt said attorneys presented prosecutors with a witness, and video evidence, which didn't capture the shooting.

Co-counsel Benjamin Crump said: "We're still dealing in America with black people being killed in some of the most arbitrary ways, driving while black, walking while black and now we have to add living.”

Crump said Jean was "living, doing everything that you want a young person to do."

"He had no criminal history. He was an amazing student. He was an amazing citizen. He loved God."

In a statement on Saturday, the police department said the Texas Rangers had taken over the investigation to "eliminate the appearance of any potential bias".

"On behalf of the Dallas Police Department, we are continuing to pray for Mr Jean's family, and ask that the community remain patient as this investigation is conducted," Dallas Police Chief Renee Hall said in a statement.

"A female Dallas police officer returned to what she believed to be her apartment after her shift ended - she was still in uniform when she encountered Mr Jean inside the apartment,"

Grant Jean, 15, and his mother Allison Jean, who are the brother and mother of Botham Jean mourn with another churchgoer during a prayer service for Jean at the Dallas West Church of Christ. (AAP)

The police chief said it isn't clear what "the interaction was between her and the victim. Then at some point she fired her weapon striking the victim."

The officer called 911 and officers "responded in about four minutes," Hall said.

"Right now, there are more questions than answers."

Alyssa Kinsey, Jean's next-door neighbour, told CNN she was home on the phone on Thursday night when she heard a shot.

She said she then heard what sounded like "running steps" and a female voice calling the police.

Kinsey said she could see from her patio that the lights were turned on in Jean's apartment.

She said she heard more footsteps outside her apartment, a woman's voice and a commotion.

The apartment doors at the complex are all similar, Kinsey said, but Jean's doorstep had a bright red mat.

She said she met Jean when she first moved into the South Side Flats in April.

Jean described himself on LinkedIn as a "young professional, engaged in developing a career built upon integrity, dedication and relationships, leveraging useful technologies to gain an understanding of and add value in a range (of) industries, striving towards leadership in my career, my community and society."

The victim’s brother, Brandt Jean, 17, said he answered the phone at home in St. Lucia when his mother Allison called and asked to speak to his father alone.

"I never heard my mother cry like that," he said.

"I still don't believe he's gone, but we have to accept it."

"He was really inspiring. He had a positive mind and vibe."

"Mainly, I will remember his advice.

"I would do stupid stuff at times and he would tell me what I needed to hear, even though it might hurt me, even though I might cry. He was real. He was down to earth."

Their mother, Allison, a former Permanent Secretary of the Department of Education, Innovation and Gender Relations for St. Lucia had been visiting New York when she learned of her son's death.

"Botham was a very wonderful young man," his father Bertram Jean said.

"His faith was very strong. We will miss our boy."

At university, Botham Jean was a "member of Good News Singers, a resident assistant, an intern for the Rock House campus ministry, and a leader in Sub T-16 men's social club," according to a statement.

At a vigil at Jean's church, the Dallas West Church of Christ on Saturday, Jean's mother, Allison said: "Botham loved mankind.

Amber Guyger shot Botham Shem Jean while off duty in Dallas and has been arrested. (Supplied)

"Botham never saw colour, never saw race. Botham wanted all of us to unite."

Jean was hired at PricewaterhouseCoopers in Dallas after an internship with the company, according to his father.

"This is a terrible tragedy," the professional services and auditing firm said via Twitter.

"Botham Jean was a member of the PwC family in our Dallas office and we are simply heartbroken to hear of his death."

"This world has lost a light in the dark," said one of Jean's coworkers.

Guyger was involved in another shooting incident in May 2017, when a suspect took her taser, according to a Dallas Police Department news release.